1. Field of the Invention
The present invention relates to a pressure developing apparatus, for example, in a copying machine, an optical printer, or the like, for developing a latent image obtained by exposing a photo/pressure sensitive sheet on which photosensitive microcapsules are applied, and particularly relates to an ultrasonic developing apparatus which employs an ultrasonic vibrator as pressure generating means.
2. Description of Prior Art
As disclosed, for example, in Japanese Patent Unexamined Publication Nos. 58-23025/1983, 58-88739/1983, ETC., known is a photo/pressure sensitive sheet in which microcapsules each containing a dye-precursor, photo-sensitive resin, etc. are dispersively applied into a paper base together with a developer which will cause a development reaction in cooperation with the die-precursor. There has been developed a photo/pressure sensitive sheet of the transfer type in which a photo-sensitive sheet onto which only microcapsules are dispersively applied and a transfer sheet onto which only a developer is applied are used in pair. The photo-pressure sensitive sheet has been promoted to be utilized for a copying machine, an optical printer, etc. For Example, when the photo/pressure sensitive sheet of the transfer type is used for the copying machine, light is radiated on a surface of an original so as to scan the surface, so that the surface of the photo-sensitive sheet is exposed to the light which has scanned the surface of the original. Succeedingly, the photo-sensitive sheet and the transfer sheet are put on each other and are passed between pressing rollers so as to break the unhardened ones of the microcapsules by pressure so that a development reaction is caused between the dye-precursor body and the developer to thereby obtain development on the transfer sheet. Accordingly, according to the photo-pressure sensitive sheet, there are such advantages that use of toner is not necessary, copied materials of high resolution can be obtained, etc.
However, when the unhardened ones of the microcapsules on the photo/pressure sensitive sheet are broken by the pressing rollers, pressure of about 500 through 600 Kg/cm.sup.2 is required between the pressing rollers because of load resisting force of the microcapsules. This value of pressure is approximately three times of that for the pressing rollers used in a conventional copying machine for ordinary paper. Therefore, there have been many disadvantages that wrinkles are produced on the sheet, the sheet is broken when foreign matters are rolled between the rollers, the surface of the sheet is made glossy owing to the high roll-pressure so as to be hardly seen.